Today
was a very busy dive day that began at noon and lasted until long past
dinnertime. We instrumented a high- and a low-temperature vent site,
collected many samples, and made some new discoveries. Because we have
placed acoustic marker beacons at most of our sites, we can now move
rapidly between them. Our first day’s target was the 12 meter-high
sulfide-carbonate spire at Rebecca’s
Roost. The summit of this structure is a series of pagoda-like flanges
that have successively broken away as the ROV attempted to park on them.
All that was left of the summit was a tall chimney on one edge of the
cliff with a connecting bridge to a “bush” of tubeworms.

We
decided to place an OsmoSampler combined with a Hobo at this site to
collect continuous fluid and temperature measurements over the next two
months. The body of the OsmoSampler is a large cylinder filled with
osmotic pumps and spools of Teflon tubing that connect to a small-bore
titanium wand. The Hobo also has a long wand within which an RTD
(temperature measuring device) resides. This thermocouple connects to a
small datalogger that is well removed from the hot water. For this
deployment, the two wands are connected together and fashioned into a
“J” shape so that everything can be hung on the edge of the chimney,
not unlike a garment bag hanging on a door.

Perching
the ROV was precarious, but parking was out of the
question. So the pilots flew up and dropped both parts of
the system onto the bridge. Flying the ROV up to the other side of the
chimney, they enlarged the orifice with a bar
brought along for this task. Then, the pilots flew the vehicle to the
bridge, grabbed the J-hook, and flew up to the vent to place the curved
wands (see left).

When
we left the site, the experiment could be seen draped around the rapidly
growing summit chimney (see right). How will these
instruments look after two months? Will we be able to pull it from the
wall of the sulfide?

The
remainder of the day’s work was at the two new low temperature sites:
Cathedral Hill found yesterday and a new vent we just stumbled across and
named Theme Park (see left). We had hoped to place thermocouple arrays at
both sites,
but one array malfunctioned and had to be returned to the ship.
Hydrothermal fluid and chimney samples were collected at Cathedral Hill
(see right) and at Theme Park (see below left). The high temperature probe
was used to locate sediments over 60˚ C and a “hot push core” was
taken from there (see below right). At the end of the day, a thermocouple
array was left at Theme Park.

When
the ROV returned, the smell of oil and rotten eggs filled the air. All of
the fluid, mud, and chimney samples from the low temperature sites were
drenched with hydrocarbons. We hurriedly moved all the chimneys outside
and put the push cores under the hoods. The amount of hydrocarbons was
amazing, bubbling to the top of the push cores (see
left - the red drops in the image are hydrocarbons) and leaving oily spots
on the mats. This was a slimy, gooey end to a successful day.